Attachment reminder

A common usage problem with email clients is that while writing an email the action of attaching a file is often forgotten. So it is very common that people send around a mail where they say that they are going to attach something, but suddenly they send out the mail without any attachment at all.

Therefore, other email clients like Thunderbird 3+ now have a feature to try to identify semi-automatically that the author of an email is going to attach a file while writing an email. In TB3 this seems to be done by searching for common words like "attachment", "Anhang", "pdf" or other words (have to be analysed/found in the TB code).

IMHO it would be a very nice thing to have a similar feature in YAM so that a warning appears similar to an empty subject warning right before a mail is sent out. However, we have to find out what TB3 is really doing to identify the case of reminding for an attachment.